Research Journal of Applied Sciences, Engineering and Technology 2(8): 757-764, 2010
ISSN: 2040-7467
© M axwell Scientific Organization, 2010
Submitted date: October 19, 2010
Accepted date: November 22, 2010
Published date: December 10, 2010
Earth Construction and Landfill Disposal Options for Slaker Grits
1
1
G. W atkins, 2 R. Pöykiö, 3 H. Nurmesniemi and 1 O. Dahl
Aalto University, School of S cience and Technolo gy, Departm ent of Forest Products
Techno logy , Laboratory of Chemical Pulpin g and Environm ental Techno logy ,
P.O. Box 16300, FI-00076 Aalto, Finland
2
City of Kemi, Valtakatu 26, FI-94100 Kemi, Finland
3
Stora Enso Oyj, Veitsiluoto Mill, FI-94800 Kemi, Finland
Abstract: Slaker grits, an industrial residue originating from the chemical recovery proce ss at sulfate (kraft)
pulp mills, are typically disposed of to landfill in Finland. However, due to the relatively low total heavy metal
and low leach able heav y metal, chloride, fluoride, sulfate, Dissolved O rganic Carbon (D OC) and Total
Dissolved Solids (TDS) concentrations, the residue is a potential earth construction material. This paper gives
an overview of the relevant Finnish legislation on the use of industrial waste as an earth construction agen t, the
classification of waste into one of three classes: hazardous waste, non-hazardous waste and inert waste, as well
as the b road waste policy goals under EU law that affec ts their manag eme nt.
Key w ords: Cau sticizing, environme ntal permit, leaching, n on-process elem ents, pulp m ill, waste
INTRODUCTION
The managem ent of solid wastes such as slaker grits,
derived from the che mical recov ery cycle of the kraft
(sulfate) pulping process, h as traditionally been v ia
landfilling. However, the rise in the costs of landfill, as a
waste management options, driven by regulation designed
to protect hum an he alth and the environme nt, has led to
problems in acquiring new sites for disposal purposes and
has increased costs for their development and operation,
such that solid waste generation represents a continuing
disposal problem for the forest industry. The utilization of
solid wastes allows industry to reduce its reliance on the
landfill options, reuse and recycle residues or even utilize
materials as beneficial produ cts in line with the objectives
of European Union laws (EC, 1991, 2006, 20 08). There
is therefore a growing trend towards seeking options for
the utilization of solid wastes in the Finnish pulp and
paper indu stry.
According to the European Council W aste
Framework Directive (WFD) (2006/12/EC) as amended
by the new W FD (Direc tive 2008/98/E C), co ming into
force in December 2010, waste policy should aim at
reducing resource usage (EC, 2006, 2008). The use of
waste prevention approaches and the re-use and recycling
of materials are therefore at the forefront of this policy,
whe re waste recovery needs to be encouraged to reduce
the use of natural resources and promote sustainability.
Article 3 of the new W FD restates the order of preferred
approach to the issue of waste called the waste hierarchy
whe re the principle of primarily focusing on the reduction
of the amount of waste produced and its harm fulness is
augmented by a secondary target of the recovery of w aste
by means of recycling, re-use and reclamation. Processes
aimed at extracting secondary raw materials are included
in this latter group. If any of these methods are not
feasible, waste should be used as a source of energy. The
safe disposal of waste via landfill is specified only as a
last resort in the priority ranking of waste management
method. A definition of recycling has also been added to
the new WFD, where “recycling” m eans “the recovery of
waste into products, materials or substances whether for
the original or other pu rpose s”.
The new W FD o ffers the possibility for more straight
forward approach to the development of residue based
products through the introduction of new concepts such as
i.e., new legal term s for substances falling between the
waste and non-wa ste (product) classifications - namely
the term side-product. Further changes under the new
WFD will see the introduction of criteria to define the so
called “end-of-waste” status (promulgation of which is to
be via a process of EC comitology or binding norms
in environmental permits). The possible categories of
waste that the new WFD recognizes as candidates for
end-of-waste criteria include construction and demolition
waste, some ashes and slags, scrap metals, aggregates,
tyres, textiles, compost, waste paper and glass. The
possibility of extending the list of end-of-waste candidates
to other residue streams (including residues such as slaker
grits) would depend upon the stream conforming to a set
of criteria:
C
The substance or object is commonly used for special
purposes
C
A market or demand exits for such a substance or
object
Corresponding Author: Dr. Risto Pöykiö, City of Kemi Valtakatu 26, FI-94100 Kemi, Finland
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Res. J. Appl. Sci. Eng. Technol., 2(8): 757-764, 2010
Fig. 1: The causticizing process as a part of pulp mill chemical recovery circuit (Järvensivu et al., 2001; modified)
C
C
The substance or object fulfills the technical
requirements for the special purposes and meets the
existing legislation and standards applicable to
products, and
The use of the substance or object will not lead to
overall adve rse environmen tal or human health
impacts.
this process is to convert inactive sodium carbonate
(Na2 CO 3 ) back into sod ium h ydroxide (N aOH), w hich is
an active c ooking ch emical, and to insure that this
conversion rate is as high as possible. The recycling and
reuse of various aqueous streams present in the sulfate
pulping process leads to the build-up of non-process
elem ents (NPEs), e.g., potassium, magnesium,
manganese, barium, iron, aluminum, copper, nickel,
chromium and zinc, the majority of which are detrimental
to the pulping, bleach ing or recovery processes. The
introduced or NPEs into the proc ess occurs via the fibre
raw materials themselves (i.e., wood chips and sawd ust),
the make-up chemicals, process waters and from the
corrosion of process equipments. The accumulation of
NPEs in the pulp m ill's bleach plant may result in scaling
problems and filtration failures, and they can also catalyse
the decomposition of bleaching chemicals, thereby
reducing bleaching efficiency (Jemaa et al., 1999). In
addition, NPEs cause operational problems such as scale
formation on washers and the plugging of process
equipment. The remova l of NPE s from the reco very cycle
is therefore necessary in order to reduce operational
problems caused by their build-up and precipitation. The
NPEs and other insoluble materials are purged from
chemical recovery cycle in the form of green liquor dregs
(from the main recovery cycle) and as slaker grits (from
make-up chemical addition) (Parthasarathy and
Krish nagopalan, 1999).
The slaker grits investigated in this study were
sampled from the outlet of the causticizing process at a
pulp mill located in Finland (Fig. 1). In 2008, the pulp
mill produced approximately 665 tonne s of slak er grits
expressed on a dry w eight (d.w.) basis, w hich w as all
disposed off to landfill. The sampling was carried out
This study looks at the characteristics of slaker grits,
their potential utilization as an earth construction material
and the legal implication o f such usage. The study is part
of a major project focusing on reducing, reusing and
recycling different waste materials originating from
Finnish pulp and paper mills (Pöykiö et al., 2006;
Nurmesniemi et al., 2007 , 2010 a, b).
EXPERIMENTAL
The Kra ft pulp ing and chem ical recovery process slaker grits sampling: Pulping is a process for separating
individ ual fibres in wood chips or recycled paper by
chem ical, semi-chemical, or mechanical methods.
Chemical pulping is dominated by two processes - the
sulfate (kraft) and the sulfite processes. In the alkaline
sulfate process, the active chemicals are sodium
hydroxide (NaOH) and sodium sulfide (Na2 S), whereas in
acid sulfite process, the active chemical in the cooking
liquor is hydrogen sulfite (HSO 3 G). Nowadays, the
alkaline sulfate (kraft) pulping process is the main
method used for the pro duction of chem ical pulp
(Monte et al., 2009 ).
The causticizing process is a part of the pulp mill's
chemical recovery system, in which the chemicals used in
the pulping process are recovered. The main purpose of
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Res. J. Appl. Sci. Eng. Technol., 2(8): 757-764, 2010
over a period of five days, where individual daily samples
of one kg were combin ed to give on e com posite sample
with a weigh t of 5 kg (wet weight). The sampling period
represented normal process operating conditions for the
pulp mill. After sampling, the samples were stored in
polyethylene bottles in a refrigerator (+4ºC). A coning
and quartering method was applied repeatedly to reduce
the grit sample to a size suitable for conducting laboratory
analyses (Gerlach et al., 2002 ).
Except for Hg, the total element concentrations in the
grits were determined w ith a Therm o Elemental IRIS
Intrepid II XDL Duo (Franklin, USA) inductively coupled
plasma optical emission spectrometer (ICP-OES). The
concentration of Hg in the grits was determined with a
Perkin Elmer Aanalyst 700 cold-vapour atomic absorption
spectrometer (Norw alk, USA) equipp ed w ith a Perkin
Elmer FIAS 400 and AS 90 plus autosampler. The
comprehensive review of the analytical methods and
instrumentation is given in our previous study
(Nurmesniemi et al., 2008 ).
Determination of the m ineral com position, physical
and chemical prope rties: For the determination of the
mineralogical composition of the grits, an X-ray
diffractogram was obtained with a Siemens D 5000
diffractometer (Siemens AG, Karlsruhe, Germany) using
CuK" radiation. The scan was run from 2 to 70 ° (2-thetascale), with increments of 0.02º and a coun ting time of 1.5
sec per step. Op erating cond itions were 40 kV and 40
mA. Peak identification was carried out with a
DIFFRA Cplus BASIC Evaluation Package PDFM aint 12
(Bruker axs, Germany) and ICDD PD F-2 Release 2006
softw are packag e (Pen nsylvania, U SA ).
Determination of pH and the Electrical Co nductivity
(EC) in the grits was carried out according to European
standard SFS -EN 13037 at a solid to liquid (i.e., ultrapure
water) ratio of 1:5. Determination of the dry matter
content of the grits was carried out according to European
standard SFS-EN 12880, in which a sample is dried
overnight to a constant mass in an oven at 105ºC. The
organic matter content, as measured by the loss-onignition (LOI), w as determined according to European
standard SFS-EN 12879, in which an oven-dried (105ºC)
sample is heated overnight in a muffle furnace (Box
Furnace, Lindberg, Blue M, Asheville, USA) at the
temperature of 550 ºC.
The Total Organic Carbon (TOC) content was
determined according to European standard SFS-EN
13137 using a Leco CH N-600 analyser (Leco Inc., U SA),
in which a sample is combusted and the evolved carbon
dioxide is measured by infrared spectrometry . A
comprehensive review of the standards, analytical
methods and instrum entation is given in our previous
study (Nurmesniem i et al., 2008 ).
Leaching procedures and determination of leachable
concentrations in extracts: For the determination of the
leachable conc entrations of S b, As, Ba, Cd, Cr, C u, Hg,
Pb, Mo, Ni, V, Zn, Se, DOC, fluoride, sulfate and
chloride in the slaker grits, the European standard SFSEN 12457-3 was used . This procedure is a two-stage
batch test at a liquid-to-solid ratio (L/S) of 2 and 8 L/kg,
with an extractant containing ultrapure water (H 2 O), and
the sum of leachable concentrations (i.e., L/S 10 L/kg) is
compared to the m aximum a llowable concentrations
which, in turn, together with the total element
concen trations determine whether the residue may be used
as an earth construction agent or whether it may be
disposed of to an inert-waste, non-hazardous waste or
haza rdous wa ste landfill.
The metal (i.e., Sb, As, Ba, Cd, Cr, Cu, Hg, Pb, Mo,
Ni, V, Zn and Se) concentrations in the extracts we re
determined with a Thermo Elemental IRIS Intrepid II
XDL inductively coupled plasma optical emission
spectrometer (Franklin, USA). Determination of the
Dissolved Organic Carbon (DOC) concentration in the
extract was carried out according to the European
standard SFS-EN 1484 using a Leco CHN-600 analyser
(Leco Inc., U SA ). Determination of the fluoride and
chloride concentrations in the extract were carried out
according to the European standard SFS-EN ISO 10304 -1
using a Dio nex ICS 2000 ion chrom atogra phy with
con duc tivity d et ec ti on (D i on ex C or p. , U S A ).
Comprehensive reviews of the standards, analytical
methods and instrumentation are given in our previous
studies (Nurmesniemi et al., 2008; Pöykiö et al., 2008 ).
RESULTS AND DISCUSSION
Determination of total element concentrations: For the
determination of total element concentrations in the
grits, dried samples were digested w ith a mixture of HCl
(3 mL) and HNO 3 (9 mL) in a CEM Mars 5
microprocessor controlled microwave oven with CEM HP
500 Teflon vessels (CEM Corp., M atthews, U SA) using
USEPA method 3051A (Y afa and Farmer, 2006). The
cooled solutions were transferred to 100 mL volum etric
flasks and the solutions we re diluted to volume w ith
ultrapure water. All rea gents and acids w ere suprapure or
pro an alysis quality.
Mineral com position, physical and chemical properties
of the slaker grits: The most important physical and
chemical properties of the slaker g rits are given in
Table 1, which are means of triplicate samples, expressed
on a dry weight (d.w.) basis. H owe ver, the standard
deviations are not given for the pH and TOC values,
because the triplicate samples had exactly the same
values. The pH of the grits was strongly alkaline (pH
13.1), and agrees with the findings of Ca bral et al. (2008),
who reported pH values between of 12.4 and 13.1 for
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Res. J. Appl. Sci. Eng. Technol., 2(8): 757-764, 2010
Table 1: Phy sical and chemical prop erties of the slaker grits
Param eter
Un it
Slak er grits
pH (1:5)
13.1
E le ct ri ca l C o n du c ti vi ty (E C )
mS/cm
94 .3± 0.3
L o ss -o n -i gn it io n (L O I ; 5 5 0º C ) % (d.w .)
1.4 ±0 .2
T o ta l O r ga n ic C ar bo n (T O C )
g/k g (d .w.)
<1 .0
D r y m a tt er co n te n t ( 10 5 ºC )
%
71 .6± 0.1
only calcite (CaCO 3 ) could be identified (Fig. 2).
Thus, our XRD data agrees with the findings of
Castro et al. (2009) and of Martins et al. (2007), who both
reported that calcite is the dominant phase in slaker grits.
How ever, we did not detect sodium carbonate (Na 2 CO 3 ×
H 2 O) as reported by Castro et al. (2009), nor the existence
of pirssonite (CaNa2 (CO 3 ) 2 × 2H 2 O), portland ite
(Ca(OH)2 )
or
wustite (FeO) as reported by
Martins et al. (2007). One reason for the differing
detection of minerals in the grits ma y be the differences
between the causticizing processes at our mill and those
at the mills investigated by C astro et al. (2009) and
Martins
et
al.
(2007),
since according to
Martins et al. (2007), the physical and chemical properties
of slaker grits vary significantly depending on the process
conditions in which the grits are formed. In pulp m ill
systems, the level of metals in process streams depends
e.g., on the intake of metals, proc ess co nfiguration and
equipment operating conditions, as well as on the type of
raw materials and the degree of closure. Thus, the
concentrations of non-process elements vary from one
mill to another (Jemaa et al., 1999 ; Gu and
Edw ars, 2004).
In this con text it is worth noting that, the XRD
spectrometer is unable to identify the amorphous ph ase
(i.e., non-crystalline matter), and its detection limit is
norm ally 1-2 % (w/w ). This is probably one reason why
we could not identify all the minerals observed by Ca stro
et al. (2009) and Martins et al. (2007 ), and w hy elemen ts
other than calcium were not identified by XRD , despite
the fact that the many other elements were measured
quantitatively by IC P-O ES (T able 2).
Tab le 2: Total element concentrations (mg/kg; d.w.) in the slaker grits
and the variation in element concentrations (mg/kg; d.w) in a
Finnish non -con tamin ated fine till s oil (S orv ari, 20 03) , as w ell
as the current limit v alue s (mg /kg; d .w.) in Finnish legislation
for max imu m allo wa ble m etal co nce ntratio ns fo r ma terials
(i.e., coal, peat and biomass-deri ved ash ) use d as an e arth
cons truction ag ent (V na, 20 06)
Finn ish so il
Elem ent
Slak er grits
(till; <0.06 mm)
Limit value
Al
15 40 .0± 43 .6
As
<3
-20
50
Ba
22 8.7 ±4 .2
400-900
3000
Ca
331333±3786
Cd
0.3
1.1
15
Co
1.1 ±0 .1
-30
Cr
12 .6± 0.4
-300
400
Cu
<10
10-70
400
K
3073±32
Mg
4910±114
Mn
27 3.3 ±5 .8
Na
35033±586
P
4217±71
Mo
<1
-2
50
Ni
23 .9± 1.2
10-100
Pb
<3
0.1-20
300
S
9630±102
V
39 .0± 0.6
30-180
400
Zn
9.9 ±0 .3
30-400
2000
Hg
<0.03
Ti
11 3.3 ±5 .8
slaker grits. The alkaline pH value means that the slaker
grits have a liming effect and are therefore a potential soil
conditioning or amendment agent. According to the
electrical conductivity value (94.3 mS/cm), which is an
index of the total dissolved electrolyte concentrations, the
leaching solution of the grits has a relatively high ionic
strength, indicating that part of the dissolved metals occur
as dissolved basic metal salts.
The Total Organic Carbon (TOC) value being lower
than 1.0 g/kg (d.w .) and the loss-on -ignition (LOI) value
of 1.4 % (d.w.) indicate that the organic matter content in
the grits is very low. However, although loss-on-ignition
(LOI) is a common and widely used method to estimate
the organic matter content of waste materials, according
to Heiri et al. (2001), reactions other than the burning of
organic matter, e.g., dehydration of clay minerals or metal
oxides, the loss of volatile compounds, or loss of
inorganic carbo n (i.e., CO 2 ) in minerals, can take place
during the determination of LOI at 550ºC. Thus, LOI is an
indirect measure of the organic matter content of the grits.
The relatively low dry m atter content (71.6%) of slaker
grits is an advantage, since dust problems during handling
are no t very likely.
Although XRD analysis can be useful in identifying
the chemical species of crystalline particles, in our case
Total element concentrations in the slaker grits: The
total element concentrations in the grits a re shown in
Table 2. The elevated sodium and sulfur concentrations
are reasonable in the light of the fact that sodium in the
form of Na 2 S, NaOH and Na2 SO 4 are cook ing ch emicals
employed in the su lfate pulping process. Sodium also
enters the system in moderate quantities in the wood raw
mate rials and fro m m ake-u p and bleaching c hem icals.
The elevated ma gnesium conc entration in the grits is
derived from the use of magnesium sulfate as an inhibitor
during an oxygen delignification process step employed
in the bleaching step at the particular m ill investigated in
this study. The elevated calcium co ncen tration is
reasonable since slaker grits are produced during the
slaking process which is a reaction of quick lime (i.e.,
calcium oxide) with green liquor (i.e., aqueous sodium
hydroxide, sodium sulfide, and sodium carbonate) in the
slaker unit (Castro et al., 2009). Furthermo re, calciu m is
also the most abun dant mineral nutrien t in wood. Copper
and zinc are trace elemen ts in the wood raw material, but
they can also originate from eq uipm ent corrosion in the
chemical recovery process an d from proce ss che micals
(Nurmesniemi et al., 2005).
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Res. J. Appl. Sci. Eng. Technol., 2(8): 757-764, 2010
Fig. 2: XRD data of the slaker grits
Tab le 3: Leachable concentrations of heavy metals, chloride, fluoride, sulfate, dissolved organic carbon (DOC ) and total dissolved solids (TDS) at
a liquid -to-so lid (L /S) ratio of 1 0 L /kg (m g/kg ; d.w ., n = 1 ) in the slake r grits a nd th e cu rrent F innis h lim it va lue s (m g/k g; d .w.) of these
compounds for ac cep tanc e as w aste a t land fills (EC , 199 9), as w ell as current Finnish limit values (mg/kg; d.w.) for these compounds for
unpaved and paved materials (i.e., coal, peat and biomass-derived ash) used as an earth construction agent (Vna, 2006)
Compound
Slak er grits
Inert w aste
Non-hazardous
Ha zard ous wa ste
Limit Value
Limit Valuec
land fill
wa ste lan dfill
land fill
(unpaved)
(paved)
As
< 0.15
0.5
2.0
25
0.50
0.50
Ba
0.58
20
100
300
20
20
Cd
< 0.01
0.04
1.0
5.0
0.04
0.04
Cr
< 0 .1
0.5
10
70
0.50
0.50
Cu
< 0 .1
2.0
50
100
2.00
2.00
Hg
< 0.005
0.3
10
30
0.01
0.01
Ni
< 0 .1
0.4
10
40
0.40
0.40
Pb
< 0.15
0.5
10
50
0.50
0.50
Sb
< 0.05
0.06
0.7
5.0
0.06
0.06
Mo
0.19
0.5
10
30
0.50
0.50
V
7.3
2.00
3.00
Se
< 0.075
0.1
0.5
7.0
0.10
0.10
Zn
< 0 .1
4.0
50
200
4.00
4.00
C l181
800
15.000
25.000
800
2400
F
<5
10
150
500
10
50
SO 4 2 5250
1000
20.000
50.000
1000
10.000
DOC
80
500
800
1000
500
500
(a)
TDS
88500
4000
60.000
100.000
(a)
: The value for total dissolved solids (TDS) can be used alternatively to the values for sulfate (SO 4 2 G) an d ch lo ri de (C lG).
Table 2 shows that the heavy metal concentrations in
the slaker grits compare well with those in Finnish soils
(Laine-Ylijoki et al., 2005; Sorvari, 2008), except for the
sodium concentration. The very low metal concentrations
support its beneficial utilization instead of final disposal
to landfill, sinc e it would be econ omically and
ecolo gically preferable if solid industrial residues and byproducts could be utilized e.g., as an earth construction
agen t. Such an approach con serves virgin raw materials
and the utilization of solid wastes and residues in
activities such as land-spreading and as an earth
construction agen t, allows industry to implement the 3R
principles of the reduction, reuse and recy cling through
the use of residue materials as beneficial prod ucts
(Yoshida et al., 2007 ).
In order to obtain information about the
concentrations of hazardous compo unds in slaker grits
and to promote their utilization, we compared the total
(Table 2) and leachable (Table 3) concentrations of
hazardous compounds in slaker grits to the limit values
for coal, peat and biomass-derived ash used as an earth
construction agent (Vna, 2006). The total concentrations
of As, B a, Cd , Cr, Cu, M o, Pb, V and Zn in slaker g rits
are clearly lower than the maximum a llowable
concentrations of these compounds in coal, peat and
biomass-derived ash used as an earth construction agent
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Res. J. Appl. Sci. Eng. Technol., 2(8): 757-764, 2010
(Table 2). This indicates that slaker grits are potential
industrial residues for utilization in earth construction.
How ever, according to the results in Table 3, the
leachable concentrations of vana dium (7.3 mg/kg; d .w.)
and sulfate (5 250 mg/k g; d.w.) in slaker grits exceeded
the limit values set for coal, peat and biomass-derived ash
used as an earth construction agent. The limit values are
2.0 mg/kg (d.w.) and 3.0 mg/kg (d.w.) for vanadium in
unpaved materials and in paved materials, respectively,
and 1000 mg/kg (d.w.) for sulfate in unpaved materials.
Although the limit values given in Table 3 are not applied
for slaker g rits, this comparison will help the
environmental authorities to assess the leachability of
haza rdous com pounds fro m slak er grits.
adverse environmental or human health impacts (new
WFD preamble 22). This means that end-o f-waste criteria
can to some extent be decided on national level and
dom estic legislation could b e forthcomin g on this.
In Finlan d, the environme ntal permit is granted by the
local municipal environmental authority if the amount of
waste to be used is lower than 5000 tonn es. For amo unts
large than 5000 tonnes, the permitting authority is the
regional environmental centre. In the case of experimental
projects, how ever, an env ironmental permit is not
nece ssarily required and a notification to the au thorities is
usua lly sufficient (Mroueh and Wahlström, 2002;
Sorvari, 2003). However, an env ironm ental permit is also
required for the utilization of coal, peat and biomassderived ash or crushed co ncrete materials in cases w here
the total and the leachable concentrations of hazardous
compounds in these residues exceed the maximum
Finnish limit values set for their utilization. Therefore, on
the grounds of the above-mentioned Finnish legislation
requirements, grits cann ot be utilized freely as an earth
construction agent, and an environmen tal perm it is
required for their utilization .
Legislative requirements for the use of slaker grits as
an earth construction agent in Finland: In Finland,
industrial residues such as ash, blast furnace slag,
concrete, used tyres, crushed glass, paving materials and
ferrosu lfate gypsum, have been used in earth construction
for decades (Mroueh and Wahlström, 2002;
Sorvari, 2003). The most extensively utilized m aterials in
earth construction are blast-furn ace slag, concrete debris
from dem olition w ork, an d power plant ash. A t the
present time, the Finnish environm ental leg islation sets
limit values for both the total and leacha ble
concentrations of certain heavy metals, and/or of chloride,
fluoride, sulfate and Dissolved Organic Carbon (DOC)
and Total Organic C arbon (TO C), if a waste material such
as coal, peat and biomass-derived ash or crushed co ncrete
are used as an earth construction agen t. How ever, if co al,
peat and biomass-derived ash are app lied as an earth
construction agen t, then the limit value for both the total
and leachable concentrations of Polychlorinated
Biph enyls (PCB) and Polycyclic Aromatic Hydrocarbons
(PAH) are also applied. These limit values, which are
presented in this study (Table 3) for coal, peat and
biomass-derived ash, came into force in July 20 06 and are
applied if the ash is used as an earth construction agent
e.g. in roads, cycling p aths, pavem ents, car parks, spo rt
fields etc., (Vna , 2006 ).
Finnish environmental legislation currently does not
recognize the concept of a “by-product” and thus, if
industrial residues other than coal, peat and biomassderived ash or crushed conc rete materials are used as an
earth construction agent, then the environmental perm it is
required (Mroueh and W ahlström, 200 2; Sorvari, 2003 ).
According to the Finnish environmental legislation, all
industrial by-produ cts and residue s are actually classified
as waste and normally anyone who intends to reprocess,
reuse, or recycle on a large scale has to apply for an
environmental permit. Howev er, the new W FD “e nd-ofwaste” criteria describe abov e, will m ake it possible for
EU member states to define in an environmental licence
or general binding norm that certain by-products have no
Classification of slaker grits for landfill disposal: The
European Council Landfill Directive 1999/31/EC
classifies all waste into one of three classes: hazardous
waste, non-hazardous waste, and inert waste (EC, 1999;
Pöykiö et al., 2009 ). In the European U nion (E U), a
hazardous classification of waste should be performed
before decisions are made o n waste landfill disposal. The
leachable concentrations of heavy metals (As, Ba , Cd, Cr,
Cu, Hg, Ni, Pb, Sb, Se and Zn), as well as the
concentrations of chloride, fluoride, sulfate, dissolved
organic carbon (DOC) and Total Dissolved Solids (TDS ),
in slaker grits are sh own in Table 3. In this context it is
worth noting that, when the decision about waste
acceptance is made, the value for TDS can be used as an
alternative to the values for sulfate and chloride
(Vna, 200 6).
According to the results in Table 3, the leachable
concentrations of all heavy metals, chloride, fluoride and
DOC in slaker grits were lower than the current EU lim it
values for these com pounds fo r acceptanc e of as waste at
inert waste landfills. However, the leachable
concentration of sulfate (5 250 mg/k g; d.w .) in slaker grits
clearly exceeded the limit value for inert w aste landfill
(1000 mg/kg; d.w.), but was lower than that for nonhazardous landfill (20.000 mg/kg; d.w.). Furthermore, the
leachab le conc entration of TDS (88.50 0 mg /kg; d.w .) in
slaker grits clearly exceeded both the limit value for inert
waste landfill (4000 mg/kg; d.w.) and for non-hazardous
waste landfill (60.000 mg/kg; d.w.), but was lower than
the limit value for hazardous waste landfill (100.000
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Res. J. Appl. Sci. Eng. Technol., 2(8): 757-764, 2010
mg/kg; d.w.). However, due to the fact that the value for
TDS can be used as an alternative to the value for sulfate
(EC, 1999), the slaker grits investigated in this study can
even be deposited in a non-hazardo us wa ste landfill. In
this context it is worth noting that, although the leached
concentration of sulfate (5250 mg/kg; d.w.) exceeded the
limit value for inert w aste landfill, according to the
Finnish legislation, wh ich is based on EU directives and
regulations, the competent environ mental authority may
decid e that the maximum limit values can be up to three
times higher than those given in Table 3 on the basis of
the local environmental conditions in a landfill
(EC, 1999). In spite of this possibility for the
environmental autho rities to relax the maxim um lim it
values for sulfate, the slake r grits inve stigated in this
study cann ot be deposited in inert waste landfill according
to local policy decisions with respect to relaxation.
How ever, the classification of slaker grits as nonhazardous waste does not restrict the use of the residue as
an earth construction agent e.g. at landfills themselves,
because, according to Sorvari (2003), a by-product that is
used in earth construction may not have the properties of
a hazardous wa ste. Future changes to Finnish waste
management laws in response to the new provisions
introduced by the EU Waste Framework Directive (EC,
2006) might also allow for wider utilization of slaker grits
for beneficial purposes if end-of-waste status criteria
could be comp lied w ith.
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At the present time, Finnish environmental legislation
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